Now that the full story of Paul Manafort’s foreign lobbying abuses has come out, one might expect lawmakers on Capitol Hill to finally follow through on their pledge to fix the nation’s broken lobbying disclosure laws.

The dirty tricks made public as part of Manafort’s recent plea deal with Special Counsel Robert Mueller capture foreign lobbying at its worst. Manafort hid millions in foreign payments from the IRS in offshore accounts, and reveled in his bare-knuckled campaign to “plant some stink” on former Ukranian Prime Minister Yulia Tymoshenko, as he put it. Manafort pled guilty to violating the Foreign Agents Registration Act (FARA), which requires lobbyists representing foreign interests to register and report their activities.

But instead of doubling down on regulating agents like Manafort, Republicans on Capitol Hill have largely abandoned their push for new foreign lobbying legislation, and are instead using FARA to go after—environmental groups. Never mind that Mueller’s guilty pleas continue to pile up, or that the nation’s election system remains as vulnerable as ever to Russian meddling. The biggest foreign threat to the U.S., some GOP lawmakers appear to have decided, comes from groups like the Natural Resources Defense Council (NRDC).

It all started in June, when the House Natural Resources Committee wrote the NRDC to complain that the environmental group was ignoring pollution in China while taking actions adversarial to the U.S., including lawsuits against the Navy for threatening marine life. Committee Chairman Rob Bishop, of Utah, and Arizona Republican Bruce Westerman, who chairs the panel’s Subcommittee on Oversight and Investigations, demanded stacks of documents within a week, and suggested that the NRDC may be a Chinese agent in violation of FARA.

Bishop and Westerman also wrote two other environmental groups, the Center for Biological Diversity and the World Resources Institute, with similar allegations and demands. The committee is investigating the “manipulation of tax-exempt 501 (c) organizations by foreign entities to influence U.S. environmental and natural resources policy to the detriment of our national interests,” states a committee letter dated September 5.

Needless to say, the environmental groups deny acting as foreign agents. “Of course we work in China,” said Bob Deans, the NRDC’s director of strategic engagement, in an email. “It’s the world’s most populous country and one of the biggest polluters.” Deans added that the NRDC will “continue to exercise our First Amendment rights to freedom of speech and to petition our government without fear of reprisal.”

Kierán Suckling, executive director of the Center for Biological Diversity, was more blunt. In one of two letters to the committee, he wrote: “If Reps. Bishop and Westerman are truly confused about the Center’s motivation and control, it is perhaps because they abuse their positions of power so regularly, and are so deeply influenced by powerful corporate donors, that they are unable to conceive of people being motivated by empathy, public interest and respect for the rule of law and democracy.”

Both Bishop and Westerman have received more than $50,000 apiece in oil and gas industry campaign contributions in this election cycle. Whatever their motivations, the Charity & Security Network, a resource center for nonprofit organizations, has warned that the lawmakers’ letter-writing “confirms civil society’s worst fears about how the Foreign Agent Registration Act (FARA) can be politicized to target nonprofits in the U.S.”

The letters recall the McCarthy era, when the Justice Department accused anti-war advocate W.E.B. Du Bois of acting on behalf of the Soviet Union in violation of FARA. (Du Bois was eventually acquitted.) They also shed light on why lawmakers on Capitol Hill, despite bipartisan agreement that FARA is not working, have stalled on reform legislation.

Despite the long list of FARA violations that have come to light in the course of Mueller’s probe, including by Manafort, by his associate Rick Gates, and by Trump’s former national security adviser, Michael Flynn, overhauling the law is proving trickier than it looks.

The difficulty lies defining who constitutes a foreign agent, and why. Eighty years after Congress enacted FARA as a tool to combat Nazi propaganda, the law remains little understood, barely enforced, and largely ignored. FARA enforcement and voluntary compliance have ticked up during the Russia investigation, but no one expects that to continue once Mueller’s work is done.

More than a dozen bills to overhaul FARA have been introduced on Capitol Hill, but none get at the central problem that plagues the law, say legal experts, namely that its definitions of who constitutes a “foreign principal” or a “foreign agent” are vague and overbroad.

Under FARA, a “foreign principal” is not just a foreign government, but any foreign individual, nonprofit or company. A “foreign agent” is anyone who acts at the “request” of a foreign principal, with or without pay, and the law covers not just political activities, but any effort to influence U.S. public opinion. Regulations have been so hazy, and enforcement so lax, that virtually no legal record sheds light on the law.

The upshot is that a host of players—from foreign-owned companies to advocates for the nonprofit sector—fear that tougher FARA enforcement would sweep up not just the Manaforts of the world, but academics, business leaders or nonprofits engaged in scholarly, commercial or humanitarian work. Repressive regimes in Hungary and Russia have also used FARA to justify cracking down on civil society groups, the International Center for Not-for-Profit law has warned.

If Congress strengthens FARA rules without also clearing up confusion over who’s covered, argue ICNL and other nonprofit advocates, that could lead to selective enforcement or political abuse. The Natural Resources Committee’s misguided campaign to threaten and intimidate environmental groups is a case in point. The panel’s misfire also underscores why Congress needs to go back to the drawing board—both to prevent future Manaforts and to protect FARA from being weaponized.